Anatomical and Histological Study of Orbital Fat and Subcutaneous Fat

Through intraoperative observation, histological analysis of specimens, and animal experiments on fat transplantation, we initially explore the histological characteristics of fat from different parts and provide theoretical support for related clinical operations.

The discarded orbital fat and subcutaneous fat tissue were collected from 18 patients who underwent upper eyelid and abdominal surgery at the same time, and 9 of them were stained with HE, Masson, and immunofluorescence to observe the histological characteristics of orbital fat and abdominal fat. The other 9 cases were transplanted to both sides of the back of 6-week-old nude mice. Samples were taken and stained 1 month and 3 months later, respectively, and the histological characteristics and fat survival after fat transplantation at different time points were observed.

First, intraoperative observation. The orbital fat of the upper eyelid was soft, fine, and easy to stretch and shape. It had a relatively complete capsule, and more blood vessels running longitudinally from back to front could be seen on the capsule. The subcutaneous fat tissue in the abdomen was fragile and difficult to shape, and could easily break and release oil when gently pinched. There was no obvious capsule, and the adipose tissue was wrapped by loose and thin fibrous intervals into larger lobular particles. Second, tissue section staining observation. The orbital fat contained more radial fibrous intervals, forming fat lobule structures of different sizes and shapes. The adipocytes in the lobules were more uniform in shape and smaller in average diameter. They contained more small blood vessels accompanied by or interspersed with fibrous septa. The number of internal fibrous separations in subcutaneous fat was small, and the cells in the lobules were densely arranged, uneven in shape, and large in diameter; the blood vessel density per unit area was much smaller than that of orbital fat ( p <0.05). Third, the general morphology of the 2 fats was observed after transplantation. Compared with subcutaneous fat, the texture of orbital fat was more pliable, the surface of the capsule was redder, and obvious blood vessels were visible. The color of subcutaneous fat was significantly yellower, and the surface of the capsule had fewer blood vessels. Fourth, histological section staining observation after fat transplantation in the 2 groups. The histological structure of the 2 grafts was similar to that before transplantation. The orbital fat graft still contained more fibrous septa and CD31-positive vascular structures, and more fat remained. However, subcutaneous fat grafts had fewer internal fibrous septa and vascular structures, and varying degrees of necrotic areas could be seen.

Compared with subcutaneous fat tissue, the orbital fat has a more delicate texture, more fibrous intervals, a more regular shape and a smaller diameter of adipocytes, and richer blood supply. The tissue structure after orbital fat transplantation is similar to that before transplantation, and it has better survival and tolerance. These differences can be used as a basis for selecting the source of fat transplantation when correcting a sunken upper eyelid.